The OVRO-LWA currently hosts LEDA, the largest
correlator (in terms of the number of input signals) ever built. This allows us to perform full
cross-correlation of 512 signal paths. This unprecedented capability coupled with the all-sky
sensitivity of a dipole antenna allows the array to image the entire visible sky as frequently
as is computationally feasible (of order once per second). Once completed, the OVRO-LWA will be
the most powerful radio telescope operational below 100 MHz.

512 input correlator (LEDA) performing full cross-correlation of 256 antennas with a
transient cluster imaging these visibilities on a 13 second timescale

Field of View

the full visible hemisphere

Resolution

~9 arcmin at 80 MHz to ~23 arcmin at 30 MHz

Science Goals

The OVRO-LWA's full cross-correlation and all-sky sensitivity is designed primarily for the
study of high redshift HI as a probe of the epoch of reionization and fast-cadence all-sky
imaging for the detection of low frequency transients, such as coherent radio emission from
exoplanets and compact object merger events. The OVRO-LWA's all-sky imaging will also enable
the detection and monitoring of coronal mass ejections from nearby stars. A significant amount
of observing time will also be devoted to solar dynamic imaging spectroscopy.

The Dark Ages and Cosmic Dawn

In the storybook picture of the universe, it all began with the big bang. A brief era of
inflation was followed by 300,000 years where the universe was filled with a radiation dominated
plasma. Soon after this radiation faded to the point where matter (dark matter, protons,
electrons, and small amounts of heavier nuclei) dominated the universe, the electrons and
protons were able to recombine and form neutral hydrogen. This is known from studying the
distant cosmic microwave background (CMB) radiation that is just now reaching us from the period
of recombination.

What follows is less well understood. There is a delay between recombination and the formation
of the first stars and galaxies. This period of time, referred to as the dark ages, is where
baryonic matter first begins to fall into dark matter halos. The first galaxies, clusters, and
superclusters all began to form at this time. Eventually stars form and explode in supernovae
that populate the universe with incrementally more heavy elements. These heavy elements make it
easier for gas clouds to cool and collapse, forming even more stars. The universe is now
awaking from the dark ages to a period of time known as the cosmic dawn.

In order to study the process of galaxy formation it makes sense to look for the most distant
galaxies possible. The further away a galaxy is, the further back in time we are seeing it.
This is problematic because distant galaxies are typically found and studied with optical and
near-infrared telescopes. At large distances, the bound-free opacity of neutral hydrogen
shrouds these galaxies from view.

The OVRO-LWA circumvents this problem by looking for highly redshifted 21 cm photons that are
characteristic of neutral hydrogen. Instead of studying the proto-galaxies themselves, the
OVRO-LWA makes it possible to study the gas around these galaxies. How do galaxies form and
develop into the wonderfully complex and beautiful systems we see today? How did they interact
with the surrounding gas during this process? When did galaxy formation start and how long did
it take? All of these questions are wide-open. However, with the OVRO-LWA at Owen's Valley, we
will begin to probe the answers to some of these questions.

The Transient Radio Sky

Time domain astronomy is a rich field with high potential for new discoveries, in all wavelength
regimes. The success of transient searches in the optical (with the Palomar Transient Factory
(PTF), the Catalina Real-time Transient Survey, the Panoramic Survey Telescope and Rapid
Response System (Pan-STARRS), etc.) and in the X-ray and gamma-ray skies (with the Swift
Gamma-Ray Burst Mission and the Fermi Gamma-ray Space Telescope) highlights the vast scientific
yield and exciting nature of time domain astronomy. The variable and transient radio sky,
however, remains relatively poorly sampled, due to the limited fields of view, sensitivity, and
survey speeds of traditional radio interferometers, despite the evidence that radio transient
phase space is equally as rich as its counterparts in other wavelengths.

The OVRO-LWA will open up the field of radio transients -- with full cross-correlation of all of
its 33,000 baselines and instantaneous imaging by a dedicated transient backend, the OVRO-LWA
will produce all-sky images every second with approximately 10 arcminute resolution in all 4
polarizations (IQUV), reaching less than 10 mJy RMS noise in a 1 hour integration. This all-sky
sensitivity means we can perform targeted transient searches as well as conduct blind surveys to
better sample the transient phase space and reveal new and exciting populations of radio
transients.

The OVRO-LWA transient search is particularly aimed at the detection of coherent radio emission
from extrasolar planets, similar to the extremely bright electron cyclotron maser emission
produced by magnetized planets in our own Solar System. The direct detection of extrasolar
planets through their auroral radio emission would provide measurements of magnetic field
strengths and rotation rate, as well as serving as an indirect probe of interior composition and
dynamics.

Satellite Imagery

People

Gregg Hallinan (Caltech)

OVRO-LWA PI

Lincoln Greenhill (Harvard/SAO)

LEDA PI

Marin Anderson (Caltech)

Grad Student

Michael Eastwood (Caltech)

Grad Student

mweastwood at astro.caltech.edu

Ryan Monroe (Caltech)

Grad Student

Acknowledgements

The OVRO-LWA is located at the Owens Valley Radio Observatory, a Caltech-operated observatory
near Bishop, California. Construction on the array began in 2012. The OVRO-LWA project was
enabled by the kind donation of Deborah Castleman and Harold Rosen.